Current ballast device



Sept. 3, 1940. L, c, S, JR 2,213,706

CURRENT, BALLAST DEVICE Filed Sept. 30. 1957 INVENTOR. LLOYD C. HOPKINS, JR.

7 w xy/y ATTORNEY.

Patented Sept. 3, 1940 PATENT OFFlCE CURRENT BALLAST DEVICE Lloyd 0. Hopkins, Jr., Jersey City, N. J assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application September 30, 1937, Serial No. 166,679

3 Claims.

My invention relates to current ballast devices, particularly to tubes for limiting current flow with variable voltages and methods of making the tubes.

The usual current ballast device comprises an envelope filled with an inert gas and containing a resistance wire or filament of a metal such as iron that passes a substantially constant current with varying voltages across the wire. A momentary increase in current following an increase in voltage increases the temperature of the wire, which, if the wire has a positive temperature coeflicient of resistance, causes the resistance of the wire to rise and limit the rise in current fiow. Since the voltage-current characteristic of a metal is determined by its operating temperature, it is important that the thermal conductivity of the environment of the metal wire, which is very largely dependent on the character and pressure of the inert gas, be accurately predetermined and fixed in manufacture and that these properties remain constant throughout the like of the ballast device.

An object of my invention is to make a ballast device with an accurately predetermined voltagecurrent characteristic which will remain constant throughout the useful life of the device.

Another object of my invention is to improve the method of manufacture of ballast devices that are rugged in construction, easy to make, and inexpensive to manufacture.

The characteristic features of my improved device and method of manufacture is defined with particularity in the appended claims, and one embodiment of the device and the method of manufacture is specifically described in the following specification and the appended drawing in which Figure 1 is a sectioned view of a completed tube embodying the characteristic features of my invention, and Figure 2 is a view of the assembled parts of my improved ballast tube prior to sealing the envelope of the tube.

The particular tube chosen for illustrating the characteristic features of my invention and shown in Figure 1 comprises two coaxial cup-shaped metal shells I and 2 joined gas-tight along their flanged rims with a ring of insulating material 3, such as lime glass or ceramic, adhesively welded to the outwardly extending flanges 4 and 5 at the rims of the shells. Ballasting resistance comprising one, two, or more resistors in parallel are electrically connected at their opposite ends to the two shells of the envelope so that the two shells respectively constitute the electrical terminals of the ballast resistance. The particular means for mounting the ballast resistance in the envelope chosen for purposes of illustration comprise a rectangular wire frame with U-shaped wire piece 6 and wire piece I insulatingly attached to the ends of the legs of the U to complete the rectangle. The adjacent ends of the two wire 5 pieces are mechanically interlocked yet electrically insulated by cylindrical insulators 8 and 9 with longitudinal grooves which engage the hooked ends of the two wire pieces as shown, the legs of the wire piece 6 being formed with a slight outward bias to resiliently hold the insulators in place.

Ballast resistance wire II), preferably of iron, coiled, and attached at opposite ends to the two pieces of the wire frame may be conveniently connected electrically between the two shells of the envelope by attaching the depending end of wire piece I to tab ll secured to shell I. Wire piece 6 is attached at its lower end to shell 2 by embedding its end in a cup of solder I 4 fixed as by welding to the bottom of shell 2. The ends of the envelope may conveniently be indented with round recesses I2 to receive holding clips of a connector similar to that used for cartridge fuses. In manufacturing my improved ballast tube the wire frame, with the ballast wires welded in place, is attached by welding to the tab l I in cup I, the cup I being placed upon inverted cup 2 with an interposed ring of glass 3 and with the downwardly extending end of wire 6 in registry with solder cup I2. To this end of wire 6 may be attached as by crimping a piece of solder I3. The parts in the assembled relations shown in Figure 2 may then be placed in a hydrogen furnace and the temperature gradually raised to free the assembled parts of occluded gases and to fill the shells with hydrogen at the pressure of the gas in the oven. Further heating softens glass ring 3 permitting the upper shell to lower by gravity bringing lower end of wire 6 and its globule of solder I3, now molten, into cup l4. After the glass has wetted and sealed together the flanges 4 and 5 of the shells the envelope may be cooled to room temperature. The pressure of the gas trapped in the finished tube is determined by the temperature and pressure of the gas at the instant the envelope is closed which, according to my invention, is conveniently determined by the temperature at which the glass welds to and unites the metal shells. The voltage-current characteristic of a ballast resistance is largely dependent on its temperature, which, in turn, is determined by the thermal conductivity or cooling properties of the gas surrounding the ballast resistance, and the thermal conductivity 5% of the gas is largely dependent upon the pressure of the gas.

The voltage-current characteristic or ballasting range of my improved ballast tube is accurately predetermined in manufacture by controlling the temperature at which the shell is sealed. An envelope sealed in hydrogen at atmospheric pressure and at a temperature of 100 C. results in a finished tube containing hydrogen at a pressure of about 19 mm. of mercury at room temperature (25). My improved device is characterized by the fact that the envelope may be simultaneously fabricated and 'filled with a gas of predetermined pressure. My improved ballast device is rugged in construction, easy to make, and inexpensive to manufacture.

I claim:

1. In the manufacture of a ballast device with two metal shells enclosing a framework with .ballast resistance comprising joining the framework to one of said shells, laying a ring of sealing material on the rim of the other of said shells, laying said one of the shells with its framework upon said ring, heating'the assembly in a gaseous atmosphere to the softening and sealing temperature of said material, lowering the upper shell to compress the softened material and to bring the framework into electrical engagement with said other of the shells.

2. In the manufacture of a ballast device with two metal shells and a ballast resistance electrically connected at its opposite ends to said shells comprising laying a ring of insulating sealing material on the rim of one of said shells, mechanically and electrically connecting one end of said resistance to the second of said shells, laying the rim of said second shell upon said ring of material and bringing the other end of said resistance with a mass of solder adjacent the wall of the first mentioned shell, heating in a selected gaseous atmosphere to a predetermined temperature to insulatingly seal gas tightly the rims of said shell and to melt the solder to join electrically said other end of the resistance to the first mentioned shell.

3. In the manufacture of a ballast device with two metal shells enclosing a ballast resistance, comprising connecting one end of said resistance to one of said shells, placing said one shell upon the second shell with a ring of insulating material between the rims of the shells and bringing the other end of said resistance with a mass of solder adjacent the Wall of the second mentioned shell, heating in an oven filled with a selected gas to a suificiently high temperature to displace undesired gas in the shells and to seal said rims gas tightly at a predetermined temperature, and to solder said other end of said resistance to said second shell.

LLOYD C. HOPKINS, JR. 

